1. Field of the Invention
The present invention relates to an improvement of a single-lens reflex camera of the TTL full-aperture metering type with which the lens can be exchanged.
2. Description of the Related Art
Single-lens reflex cameras of the TTL full-aperture metering type with which the lens can be exchanged have been conventionally known.
FIG. 1 is a front view showing a camera body 1 of the single-lens reflex camera, and FIG. 2 is a top view showing the camera body 1. In FIG. 1, reference numeral 2 denotes a lens mount attachment part; 3, a shutter button; 4, a strobe housing part; and 5, a quick-return mirror. In FIG. 2, reference numeral 6 denotes a main power switch; 7, a liquid crystal type display part; and 8, a hot shoe.
A camera lens mount 9 shown in FIG. 3 is attached to the lens attachment part 2, and includes a camera lens 10, an aperture ring 11 and a driving force transmission mechanism (not shown) for focus drive of the camera lens 10. The camera lens mount 9 also includes a plurality of aperture blades 12 and six electric contact pins 9a to 9f. On the other hand, the lens mount attachment part 2 includes seven electric contact pins 2a to 2g, and five of those seven electric contacts 2a to 2g are connected to the electric contact pins 9a to 9e of the camera lens mount 9.
The camera body 1 thus organized is adaptable to various types of camera lens mounts 9 that are attached to the lens mount attachment part 2 of the camera body 1.
Table 1 shown below indicates the combinations of the full-aperture F No. and minimum F No. of the camera lens to be mounted onto the lens mount attachment part 2. The information on the full-aperture F No. and the minimum F No. is represented by the combinations of H (high) and L(low) levels of the electric contact pins 9a to 9e so that the full-aperture F No. (Fmin) and the minimum aperture F No. (Fmax) are given to the camera body 1 side. Among those electric contact pins 9a to 9e, for example, three electric contact pins 9a to 9c are allocated to the full-aperture F No. (Fmin) whereas two electric contact pins 9d and 9e are allocated to the minimum F No. (Fmax).
TABLE 1 ______________________________________ Fmax 2 1 2 1 2 1 2 1 Fmin 3 2 1 H H L L L H H L ______________________________________ L L L NG 1.2-22 1.7-32 2.4-45 L L H NG 1.4-22 2-32 2.8-45 L H L 1.2-16 1.7-22 2.4-32 3.5-45 L H H 1.4-16 2-22 2.8-32 4-45 H L L 1.7-16 2.4-22 3.5-32 4.5-45 H L H 2-16 2.8-22 4-32 5.6-45 H H L 2.4-16 3.5-22 4.5-32 6.7-45 H H H 2.8-16 4-22 5.6-32 8-45 ______________________________________
The camera lens mount 9 also includes an aperture linking rod 13 that is rotated by the aperture ring 11, and the lens mount attachment part 2 also includes a coupled rod 14 that engages with the aperture linking rod 13. The camera is designed in such a manner that a resistance AVVR of a volume (not shown) changes with the movement of the coupled rod 14, and that a change of the resistance AVVR of the volume is detected to detect the aperture value equivalent of the camera lens. The aperture blades 12 are constantly urged in the minimum aperture direction by a spring means (not shown) disposed inside of the camera lens mount 9 in such manner that when the aperture ring 11 is at a position "A", the aperture blades 12 are in a minimum aperture state in the condition where the camera lens mount 9 is removed from the camera body 1.
Numerical values indicative of the F Nos. corresponding to the aperture values are marked at each of predetermined angles on the aperture ring 11, and symbol "A" indicative of control at the camera body side is marked at a position past the minimum aperture value in the direction along which the aperture ring 11 is rotated. The lens attachment part 2 also includes an engaging lever 16 that engages with a rotating lever 15 of the camera lens mount 9 in such a manner that the aperture blades 12 are rotated by the rotation of the rotating lever 15. When the camera lens mount 9 is rotated after the camera lens mount 9 is attached onto the lens mount attachment part 2, the rotating lever 15 engages with the engaging lever 16, and when the camera lens mount 9 is further rotated in the same direction, the rotating lever 15 is rotated in the full-aperture direction so that when the camera lens mount 9 is set in the lens mount attachment part 2, the aperture blades 12 becomes in the full-aperture condition.
When in the condition where the camera lens mount 9 has been attached onto the camera body 1, the aperture ring 11 is rotated in a direction indicated by an arrow Q from the position "A" indicative of control at the camera side to a position "M" indicative of control at the lens side, that is, toward the position marked with the numeric values indicative of the full-aperture F No., the aperture linking rod 13 is rotated so that the coupling rod 14 is rotated in accompaniment, to thereby change the resistance AVVR of the volume. As a result, the aperture value equivalent is transmitted as described above. In this example, if the aperture ring 11 is positioned at the position "A", the electric contact 9f changes from "H" to "L" in level, to thereby transmit the information indicating that the lens is at the position "A" to the camera body 1.
When the aperture ring 11 is rotated in the angular range corresponding to the numerals indicative of the F Nos. and then set manually to a desired aperture value in a state where the camera lens mount 9 has been removed from the camera body 1, the aperture blades 12 is rotated according to the rotation of the aperture ring 11, to thereby set the aperture blades 12 to an opening angle corresponding to the desired aperture value.
In the single-lens reflex camera thus organized, a metering switch is turned on so that metering is performed in the full-aperture condition when the shutter button 3 is depressed halfway. If an automatic exposure mode has been selected, calculations related to automatic exposure are executed according to an aperture-priority mode, a shutter-speed-priority mode, a program-priority mode or other modes.
For example, when a standard lens (with an F No. of 1.4 and focal length of 50 mm) is mounted onto the camera body 1 under the conditions where the aperture-priority mode is set, the exposure value is Ev, the metering output is Bv, the film sensitivity is Sv, and the aperture value is Av, the shutter speed Tv is calculated in principle by the following equation. EQU Ev=Bv+Sv=Av+Tv
If a lens other than the standard lens is mounted onto the camera body 1, the metering output Bv determined for a subject of a certain luminance through the standard lens differs from the metering output Bv determined for a subject of the same luminance when the lens other than the standard lens is mounted because the full-aperture F No. values differ between those two lenses. To give this difference in metering output as compensation information, the conventional device is designed such that an angle from the full-aperture position is shifted as shown in Table 2, and only angle information is transmitted to the camera body side.
TABLE 2 ______________________________________ ##STR1## ______________________________________
Table 2 indicates a case where a lens with an F No. of 2.8 and focal length of 100 mm is mounted, for example, as an arbitrary other lens shown in Table 1. For example, when the full-aperture F No. of the arbitrary lens is selected to be "8", the calculation described above is executed upon deeming that the full-aperture F No. 4 was selected with the standard lens.
This arrangement is convenient in that compensation can be performed for each lens other than the standard lens by interlocking with an aperture setting member without transmission of the full-aperture metering output error information as independent information to the camber body 1. That is, when the lens mount 9 of each lens is attached onto the mount attachment part 2, the full-aperture metering error information can be compensated by only the angle information (resistance AVVR).
In recent years, a new type of camera is being developed with which the characteristic information on the lens characteristics (full-aperture F No., minimum aperture value information, focal length information, full-aperture metering error information, etc.) are transmitted to the camera body only by a communication means. Although the volume is abolished in this new type of camera, when an old type of lens adapted to the old type of camera with a volume and having no communication means is mounted, it is impossible to obtain the full-aperture metering error information as angle information, with the results that the metering error occurs, and an appropriate exposure is not obtained when photography is performed in the automatic exposure mode.
In the case where a new type of lens adapted to the new type of camera is mounted on the camera of the old type, and the new type of lens has no aperture linking rod, no full-aperture metering error information likewise is provided as angle information, with the results that a metering error occurs, and no appropriate exposure is obtained when photograph is performed in the automatic exposure mode.
In those cases, an exposure error occurs with the new type of camera if photography in the automatic exposure mode is carried out with the control at the camera body side being set to the automatic exposure mode and the position of the aperture ring of the lens side being set to a position (position "M") other than the position "A" that signifies control at the camera body side. Thus, measures must be taken to disable selection of the automatic exposure mode or to cancel the selection of the automatic exposure mode or perform release lock if the automatic exposure mode is selected, etc. However, for a user, it is preferable in terms of ease of use to be able to execute photography in the automatic exposure mode.